linux-kernel - Re: reset during bootup

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Date:	Sun, 12 Aug 2007 13:09:04 +0200
From:	Paolo Ornati <ornati@...twebnet.it>
To:	"Dan Merillat" <dan.merillat@...il.com>
Cc:	"Linux Kernel Mailing List" <linux-kernel@...r.kernel.org>
Subject: Re: reset during bootup - solved

On Sun, 12 Aug 2007 05:44:36 -0400
"Dan Merillat" <dan.merillat@...il.com> wrote:

> However, a git-pull at 2am (b8d3f244) fixed it.  Not sure where in
> there it started working again, I can bisect backwards to find out if
> need be.

I think it is was fixed by this one:

----

    Do not replace whole memcpy in apply alternatives
    
    apply_alternatives uses memcpy() to apply alternatives.  Which has the
    unfortunate effect that while applying memcpy alternative to memcpy
    itself it tries to overwrite itself with nops - which causes #UD fault
    as it overwrites half of an instruction in copy loop, and from this
    point on only possible outcome is triplefault and reboot.

b8d3f2448b8f4ba24f301e23585547ba1acc1f04
 arch/x86_64/lib/memcpy.S |    4 +++-
 1 files changed, 3 insertions(+), 1 deletions(-)

diff --git a/arch/x86_64/lib/memcpy.S b/arch/x86_64/lib/memcpy.S
index 0ea0ddc..c22981f 100644
--- a/arch/x86_64/lib/memcpy.S
+++ b/arch/x86_64/lib/memcpy.S
@@ -124,6 +124,8 @@ ENDPROC(__memcpy)
 	.quad memcpy
 	.quad 1b
 	.byte X86_FEATURE_REP_GOOD
-	.byte .Lfinal - memcpy
+	/* Replace only beginning, memcpy is used to apply alternatives, so it
+	 * is silly to overwrite itself with nops - reboot is only outcome... */
+	.byte 2b - 1b
 	.byte 2b - 1b
 	.previous

-- 
	Paolo Ornati
	Linux 2.6.23-rc2-gac078602 on x86_64
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